This invention relates to a method of surface finishing and, more particularly, to a vibratory method for producing a refined surface roughness on a metal component.
For selected metal components such as a gear, bearing, or spline of a power transmission, it is desirable to refine the surfaces of the components. A component having a refined surface provides greater durability from the increased contact area and lower contact stress that results from the surface refinement. In addition, the lambda ratio, λ, defined to be the lubricant film thickness divided by the composite surface roughness, increases as the surface roughness is reduced, which results in greater surface durability of gear and bearing components.
Conventionally, grinding and polishing equipment is used to improve the surface finish of a metal component. Grinding and polishing provide only a limited degree of surface refinement, often leave undesirable particles on or impregnated in the metal surface, and generally require long periods of time. Although effective in coarse surface refinement, grinding and polishing may often be unfeasible for achieving a highly refined surface, which provides significant benefits for power transmission power throughput. Grinding and polishing are subject to certain limitations or increased costs in the preparation of surfaces that present complex shapes, such as the working surface of a power-transmission gear.
Another conventional surface finishing method includes use of a chemical mixture and vibration to refine metal surfaces. The chemical mixture includes substances such as oxalic acid, sulfuric acid, chromates, phosphates, stabilizers, wetting agents, abrasive particles, or mixtures thereof. Vibratory equipment holds the chemical mixture and metal components. The rough surfaces of the components are wetted with the chemical mixture which reacts with a surface layer of the metal component to form a soft reaction layer. The vibratory equipment agitates the component and chemical mixture. The agitation produces relative movement between the component and the abrasive particles and continuously oxygenates the chemical mixture. The relative movement between the components and abrasive particles scours higher elevations (peaks) of the soft reaction layer away. The scouring occurs primarily on the most elevated portions (peaks) and results in refinement of the surface. Although this is effective for surface refinement, an undesirable residual soft reaction layer remains on the metal component surface. Furthermore, the chemical substances, especially chromate and phosphate containing substances may entail undesirable waste treatment management.
A related conventional finishing method utilizes an additional burnishing step to remove the remaining soft reaction layer and neutralize the chemical mixture. The burnishing method includes use of a separate second solution. The second solution is an inert aqueous alkaline soap mixture that includes burnishing particles. The metal component is agitated in the inert mixture after the chemical mixture surface refinement step to physically remove the soft reaction layer and neutralize remaining chemical mixture from the previous refinement step. The abrasive action of the burnishing particles in inert mixture, however, can be counterproductive to surface refinement. Furthermore, the added burnishing step using a separate second solution can add significantly to the expense and time of the entire surface finishing process.
Another conventional burnishing method utilizes an acid, such as hydrochloric acid, to dissolve the soft reaction layer. Use of hydrochloric acid poses concerns, such as increasing the risk of hydrogen embrittlement of the metal, particularly iron and its alloys. Also, if not controlled properly the acid may etch the surface of the component and negate the surface refinement. Furthermore, strong acids may entail undesirable waste treatment management.
Despite grinding, polishing and other existing conventional vibratory methods, a demand remains for an inexpensive and convenient surface refining process. Accordingly, it is desirable to provide a convenient surface refining method utilizing a single mixture.